Automatic instrument detection for surgical navigation

ABSTRACT

An identification system for surgical navigation is described. The navigation system contains an instrument assembly containing a coil (of a receiver) having an interior space, an instrument configured to be removably coupled to the coil, and a prong affixed to the instrument and configured to be at least partially disposed within the interior space of the coil when the instrument is coupled to the coil. The prong can have a length corresponding to the physical dimensions of the instrument. The navigation system can also contain a transmitter located within the body of a patient. The navigation system can be used to identify interchangeable instruments. Other embodiments are described.

FIELD

This disclosure relates generally to identifying interchangeable instruments, and more particularly to automatically identifying interchangeable instruments for electromagnetic tracking systems.

BACKGROUND

Electromagnetic tracking systems have been used in various industries and applications to provide position and orientation information relating to objects. For example, electromagnetic tracking systems may be useful in aviation applications, motion sensing applications, retail applications, and medical applications. In medical applications, electromagnetic tracking systems have been used to provide an operator (e.g., a physician, surgeon, or other medical practitioner) with information to assist in the precise and rapid positioning of an instrument (such as a medical device, implant, tool, or other implement) located in or near a patient's body during image-guided surgery. The electromagnetic tracking system provides positioning and orientation information for an instrument with respect to the patient's anatomy or to a reference coordinate system. The electromagnetic tracking system provides intraoperative tracking of the precise location of the instrument in relation to multidimensional images of a patient's anatomy. As the instrument is positioned with respect to the patient's anatomy, the displayed image is continuously updated to reflect the real-time position and orientation of the instrument being used.

The known physical size and shape of the instrument can be used to calculate the location and orientation of each portion of the instrument, which is then used, in turn in generating and displaying the real time position of each portion of the instrument. The combination of the image and the representation of the tracked instrument provide position and orientation information that allows a medical practitioner to manipulate the instrument to a desired location with an accurate position and orientation and display that location along with other reference structures or anatomy.

When different instruments are used with electromagnetic tracking systems, the system must be calibrated to the known physical size and shape of the particular instrument being used so it will be properly represented on the display. Hall-effect sensors in a receiver and permanent magnets organized in a particular pattern in the instruments have been used to identify the different instruments.

SUMMARY

This application relates generally to an automatic identification system for surgical navigation. The navigation system contains an instrument assembly containing a coil (of a receiver) having an interior space, an instrument configured to be removably coupled to the coil, and a prong affixed to the instrument and configured to be at least partially disposed within the interior space of the coil when the instrument is coupled to the coil, where the prong has a length corresponding to physical dimensions of the instrument. The navigation system can also contain a transmitter located within the body of a patient. The navigation system can identify interchangeable instruments by providing one or more instruments each having a prong of a length corresponding to the physical dimensions of the instrument, providing a receiver configured to be coupled to the one or more instruments, the receiver having a coil with a depth; and identifying if the one or more instruments is coupled to the receiver based on the length of the prong when the one or more instruments is coupled to the receiver.

BRIEF DESCRIPTION OF THE DRAWINGS

The following description can be better understood in light of the Figures, in which:

FIG. 1 shows a schematic of some embodiments of an exemplary electromagnetic surgical navigation system;

FIG. 2 shows a side perspective view of some embodiments of an exemplary sensor and instrument;

FIGS. 3-5 show cross-sectional views of some embodiments of exemplary sensors and instruments; and

FIG. 6 shows a schematic representation of circuitry in some embodiments for identifying different instruments coupled to a sensor.

The Figures illustrate specific aspects of the described systems and methods for automatic instrument detection for surgical navigation. Together with the following description, the Figures demonstrate and explain the principles of the structures, methods, and principles described herein. In the drawings, the thickness and size of components may be exaggerated or otherwise modified for clarity. The same reference numerals in different drawings represent the same element, and thus their descriptions will not be repeated. Furthermore, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the described devices.

DETAILED DESCRIPTION

The following description supplies specific details in order to provide a thorough understanding. Nevertheless, the skilled artisan will understand that the described systems and methods for identifying interchangeable instruments can be implemented and used without employing these specific details. Indeed, the described systems and methods for identifying interchangeable instruments can be placed into practice by modifying the described systems and methods and can be used in conjunction with any other apparatus and techniques conventionally used in the industry. For example, while the description below focuses automatically identifying different instruments used with surgical navigation systems, the methods and systems for automatically identifying instruments may be used in other systems requiring interchangeable instruments.

In addition, as the terms on, disposed on, attached to, connected to, or coupled to, etc. are used herein, one object (e.g., a material, element, structure, member, etc.) can be on, disposed on, attached to, connected to, or coupled to another object—regardless of whether the one object is directly on, attached, connected, or coupled to the other object or whether there are one or more intervening objects between the one object and the other object. Also, directions (e.g., on top of, below, above, top, bottom, side, up, down, under, over, upper, lower, lateral, orbital, horizontal, etc.), if provided, are relative and provided solely by way of example and for ease of illustration and discussion and not by way of limitation. Where reference is made to a list of elements (e.g., elements a, b, c), such reference is intended to include any one of the listed elements by itself, any combination of less than all of the listed elements, and/or a combination of all of the listed elements. Furthermore, as used herein, the terms a, an, and one may each be interchangeable with the terms at least one and one or more.

FIG. 1 shows some embodiments of an electromagnetic surgical navigation system 10. The electromagnetic surgical navigation system 10 may comprise a transmitter 20 attached to a particular anatomy of interest (i.e., a part of a patient 5), a processor 30, a display 40, and a sensor and instrument assembly 100 containing an instrument 110. Signals from a transmitter 20 and a receiver 120 may be sent to the processor 30. The transmitter 20 may include an array of one or more transmitter coils (not shown in FIG. 1). The receiver 120 may also include an array of one or more receiver coils (not shown in FIG. 1). The processor 30 may include electronics to generate a current drive signal for the one or more transmitter coils and to measure the mutual inductances between transmitter and receiver coils, and a computer to calculate the position and orientation of the receiver 120 with the respect to the transmitter 20 (or vice versa).

For example, in some embodiments each of the receiver 120 and the transmitter 20 may include coil assemblies with a trio of orthogonal and collocated coils that are arranged in particular positions and orientations to determine movements and positions of the coils assemblies relative to each other. Similarly, coil sizes and number of windings may differ between receiver and transmitter coil assemblies, as well as among the various coils in a coil architecture trio, as desired. In some embodiments, the processor 30 may include memory with physical dimensions of various instruments, such as for the different instruments shown in FIGS. 3-5. The processor 30 may further include sensors or input capabilities to store the physical dimensions of new instruments or connectivity to other computers, networks, or databases where information to provide the physical dimensions of various instruments may be available, depending on the instrument 110 being used.

In order to determine the location of the receiver 120, an alternating current drive signal may be provided to each coil of the transmitter 20. This generates an electromagnetic field that is emitted from each coil of the transmitter 20. The electromagnetic field generated by each coil in the transmitter 20 may induce a voltage in each coil of the receiver 120. These voltages may be indicative of the mutual inductances between the coils of the transmitter 20 and the coils of the receiver 120. These voltages and mutual inductances may be sent to the processor 30 for processing. The processor 30 may use these measured voltages and mutual inductances to calculate the position and orientation of the coils of the transmitter 20 relative to the coils of the receiver 120, or the coils of the receiver 120 relative to the coils of the transmitter 20, including six degrees of freedom (x, y, and z measurements, as well as roll, pitch and yaw angles).

The calculated position and orientation of the receiver 120 with respect to the transmitter 20, along with known physical dimensions of the instrument 110 based on the prong 112 (as described below), and the physical location and dimensions of the anatomy of the patient 5, may be used to calculate the position of any portion of the instrument 110 with respect to the anatomy of the patient 5. The calculated positions and orientations may then be displayed on display 40 for use by a physician in properly using instrument 110 on patient 5.

FIGS. 2-5 illustrate some embodiments of instrument assemblies 100 containing an instrument 110 and a receiver 120. As shown in FIG. 2, the receiver assembly 100 may include an instrument 110 attached to the sensor 120. The sensor 120 may be electronically coupled to processor 30 through cord 150. The instrument 110 may include an opening 118 configured to accommodate the sensor 120 and provide some structure to assist in holding the sensor 120 in place with the instrument 110.

The instrument 110 may be formed of any suitable material for use as a tool, medical instrument, etc. For example, when used as a medical instrument, the instrument 110 may comprise any material suitable for use as a medical instrument, including plastics, metals, or combinations thereof.

In the embodiments shown in FIGS. 2-5, the instrument assembly 100 may also include a tool 160. In FIGS. 3-5 different tools 160 a-160 c are shown for the purpose of representing examples of interchangeable instruments 110 and do not necessarily represent any particular tool or instrument that may be used with the electromagnetic surgical navigation system 10. As such, tool 160 may be any portion of an instrument 110 that may be used with the receiver assembly 100. The specific tools 160 a, 160 b, and 160 c are described in detail below.

The instrument 110 may also include a prong 112. The prong 112 may be formed of any material sufficient to affect the impendence of the coil 126 as described in detail below. For example, in some embodiments the prong 112 may be formed from a ferromagnetic material, medical-grade stainless steel, or other suitable material such as ferrite.

The prong 112 may have a length selected based on the type of instrument 110 or tool 160. In some embodiments, the prong may have a length ranging from about 2 mm to about 10 mm. For example, as shown in FIG. 3, the instrument contains a prong 112 a having an exposed prong length of d_(a). The prong length (i.e., d_(a) in FIG. 3) may cooperate with the coil 126 to provide identification to processor 30 that the instrument 110 contains a tool (i.e., 160 a in FIG. 3) having a particular physical size and shape. The size and shape of various instruments may be stored into memory and accessible by processor 30 for use in deriving position information of the instrument 110. Thus, the particular physical size and shape of the tool (i.e., 160 a) may be determined by the size of the prong (i.e., 112 a). Similarly, the prong length d_(b) of the prong 112 b may correspond to the tool 160 b in FIG. 4 and the prong length d_(e) of the prong 112 c may correspond to the tool 160 c in FIG. 5.

The prong 112 may be contained in the body of the instrument 110 such that it is securely attached to the instrument 110. In some embodiments, the prong 112 may be co-molded with the instrument 110 as the instrument 110 is formed. In such embodiments, the prong 112 may contain a protrusion that helps to secure the prong 112 into the instrument 110 without allowing the prong 112 to fall out of or otherwise move with respect to the instrument 110. In other embodiments, the prong 112 may be bonded to the instrument 110 with adhesive, press-fit, or other technique to couple the prong 112 to the instrument 110. In yet other embodiments, the prong 112 may be attached or connected to the instrument by screwing it into a threaded hole.

The instrument assembly 100 may also include receiver 120. The receiver 120 may include a sensor 122, a prong hole 124, and a coil 126, as shown in FIGS. 3-5. In some configurations, the receiver 120 may be formed using a thermoplastic resin encapsulating the various interior components of the receiver 120 while leaving the pronghole 124 open for positioning of the prong 112. In other configurations, the receiver 120 may formed of multiple components such that the interior is accessible for assembly of the receiver 120, and, in some instances, for repair, recalibration, or replacement of various components of the receiver 120.

The receiver 120 contains a sensor 122 which may contain one or more coils (as described herein) and may work in conjunction with the transmitter 20 and the processor 30 (as described herein) to help establish a position of instrument 110 relative to the patient 5. The sensor 122 and the coil 126 may be electrically connected to the processor 30 through the conductors 128, which may be housed in the cord 150 and in the receiver 120.

The receiver 120 also contains a coil 126. The coil 126 may be placed around the pronghole 124 (i.e., by winding) in the embodiments illustrated in FIG. 3-5. The prong 112 may then be inserted into the pronghole 124 so that the coil 126 surrounds the prong 112. The receiver 120 and the instrument 110 can be connected to each other by any suitable connection elements or techniques to form the instrument assembly 100. For example, the receiver 120 and the instrument 110 may be coupled using detents, latches, access door, strap, pin, etc.

In some embodiments, the coil 126 may be multiple coils. Impedance of each of the multiple coils may be measured separately or collectively to achieve increased sensitivity to different lengths of the prong 112. Each of the multiple coils may have similar or different configurations, yielding varying impedance response profiles, which can be used to further differentiate different prongs. Multiple coils may provide for a response that resembles a digital response to a particular prong length. In some embodiments, the configuration of the coil 126 used in the receiver 120 may be selected for sensitivity. For example, the impedance of coil 126 when the prong 112 is present in the pronghole 124 may be determined in order to indicate to the processor 30 the specific type of instrument 110 attached to receiver 120. As described herein, different lengths of the prong 112 may affect the measured impedance of the coil 126.

In the illustrated embodiments, a coil having a particular number of windings of a particular thickness and physical properties may be selected such that when different lengths of prongs are inserted into the coil, the coil inductance changes depending on the length of the prong. As such, different length prongs provide different inductances, which correspond to coil impedance. The inductance can be measured, which can indicate the length of the prong in the coil. The length of the prong may then be used to identify the specific type of instrument being used.

The following example demonstrates how the coil impedance and inductance may be used to determine prong length to identify a particular instrument 110. The coil impedance may be determined using formula (I)

Z _(COIL) =R _(COIL) +jwL _(COIL)  (I)

where Z_(COIL) is the measured voltage/measured current, R_(COIL) is the DC resistance of the coil, L_(COIL) is the coil inductance, j is the imaginary unit with the property j*j equal to −1, and w is the angular frequency of the driving voltage and is equal to 2πf, where f is the driver voltage frequency.

Prior to attaching the instrument 110 to the receiver 120, L_(COIL) may be measured as that of an air-core solenoidal coil. It can be calculated according to formula (II)

L _(COIL) =K(h)mu ₀ N ² A/h  (II)

where K(h) is the Nagaoka coefficient for coil length h, mu₀ is permeability of free space, N is the number of coil turns, and A is the coil cross sectional area. When the instrument 110 is attached to the receiver 120, the prong 112 enters the coil 126 by an instrument-specific distance d (such as d_(a), d_(b), d_(c), as described herein and shown in FIGS. 3-5). Since the relative permeability of the prong material (mu) is greater than that of air, the coil inductance increases. As a result, the phase and magnitude of Z_(an) changes. For an attached instrument, the coil inductance can be approximated using formula (III)

−L _(COIL) =K(h−d)mu ₀ [N[h−d]/h] ² A/[h−d]±mu _(prong) F _(L) mu ₀ [Nd/h] ² A/d  (III)

which can be simplified to the formula (IV)

L _(COIL) =K(h−d)mu ₀ N ² A[h−d]/h ² ±mu _(prong) F _(L) mu ₀ N ² Ad/h ²  (IV)

and further simplified to the formula (V)

L _(COIL) =N ² mu ₀ A/h ² [K(h−d)[h−d]±mu _(prong) F _(L) d]  (V)

where mu_(prong) is the apparent relative permeability of the prong which depends on mu and the ratio of prong length and diameter, and F_(L) is a factor that depends on the ratio of the prong length d and the pronghole depth h.

For example, in the embodiments shown in FIG. 4, the following values for an instrument with a 5 mm prong can be assumed: h=10 mm; coil core diameter=2 mm; N=500; mu=10 (stainless steel); mu_(prong)=5.5; d_(c)=5 mm; K(h)=0.91; K(h−d)=0.84; and F_(L)=0.72. For these values, L_(COIL) prior to the instrument attachment is L_(COIL)=0.09 mH. After the instrument attachment, a value of L_(COIL)=0.24 mH is obtained. Assuming a coil wire thickness of 42 AWG, the DC resistance of approximately R_(COIL)=20 Ohms is obtained. If the coil is driven at a frequency of f=10 kHz, the value obtained prior to instrument attachment is Z_(COIL)=20 Ohms+j 5.6 Ohms. After attachment, the value obtained is Z_(COIL)=20 Ohms+j 14.9 Ohms. Thus, the magnitude of Z_(COIL) increased by a factor of about 1.2, and the phase increases from about 15.6 degrees to about 36.7. Such an increase is well above the resolution of available current and voltage measurement technology.

Thus, the sensitivity of Z_(COIL) may be affected by the prong length, d. The higher this sensitivity, the easier it may be to differentiate between prongs 112 of different lengths (such as the prongs 112 a, 112 b, and 112 c of FIGS. 3-5). A higher sensitivity may indicate that more distinct instrument geometries (i.e. prong lengths) may be accommodated for a given coil depth. The sensitivity to the prong length d may be partially derived from L_(COIL) as delta L_(COIL)/delta d=N² mu₀A/h² [mu_(prong) F_(L)−K(h−d)] which is 0.031 mH/mm. In terms of Z_(COIL), a delta Z_(COIL)/delta d=jw 0.031 mH/mm is obtained. For a given frequency of 10 kHz, a delta Z_(COIL)/delta d=j 1.9 Ohms/mm is then arrived at. In summary, the sensitivity to various prong lengths d may be increased by increasing frequency, or choosing a prong material with higher permeability. And increasing sensitivity may allow for a wider range of prong lengths to more accurately identify different types of instruments and instruments configurations.

In some configurations, the instrument assembly 100 may include more than one prong 112 and corresponding additional coils 126. The additional prongs 112 may be of the same or different lengths to further provide variation in the possible numbers and variety of instruments 110 that may be used with the receiver 120. The additional prongs 112 may also function to releasably secure the receiver 120 to the instrument 110. The instrument assembly 100 may also include other features (not shown) that hold the receiver 120 to the instrument 110, such as detents, bias clips, bands, etc., or any feature that would removably hold receiver 120 in contact with instrument 110.

FIG. 6 shows a simplified circuit 200 that may operate to determine the inductance of the coil 126, Z_(COIL)=R_(COIL)+jwL_(COIL) in some embodiments. V₁ may measure voltage across the coil 126, and V₂ may be used to determine coil current. The current signal may be measured by sensing the voltage across resistor R_(Sens). The AC voltage V_(Drive) may energize the coil 126.

Thus, by using different prong lengths, permeabilities, etc., instruments with various configurations and types can be easily and automatically identified by electromagnetic surgical navigation system 10. The prong and coil configurations described herein offer the advantage of a simple, reliable, and compact automatic instrument identification system for interchangeable instruments. Because of the robust design of a prong and encased coil, instruments and receivers may be used multiple times without significant risk of misidentification.

The automatic identification system described herein may simplify the process for a user to use and calibrate. Conventionally, when different instruments are used with electromagnetic tracking systems, the system must be calibrated to the known physical size and shape of the particular instrument being used so it will be properly represented on the display. Hall-effect sensors in a receiver and permanent magnets organized in a particular pattern in the instruments have sometime been used to identify the different instruments. However, the Hall-effect sensors can require significant space requirements necessitating a large receiver, and the permanent magnets may become dislodged or otherwise unaligned such that proper identification of the instrument may be compromised.

In addition to any previously indicated modification, numerous other variations and alternative arrangements may be devised by those skilled in the art without departing from the spirit and scope of this description, and appended claims are intended to cover such modifications and arrangements. Thus, while the information has been described above with particularity and detail in connection with what is presently deemed to be the most practical and preferred aspects, it will be apparent to those of ordinary skill in the art that numerous modifications, including, but not limited to, form, function, manner of operation and use may be made without departing from the principles and concepts set forth herein. Also, as used herein, the examples and embodiments, in all respects, are meant to be illustrative only and should not be construed to be limiting in any manner. 

1. An instrument assembly, comprising: a coil having an interior space; an instrument configured to be removably coupled to the coil; and a prong affixed to the instrument and configured to be at least partially disposed within the interior the coil when the instrument is coupled to the coil, wherein the prong has a length corresponding to the physical dimensions of the instrument.
 2. The assembly of claim 1, wherein the coil has an inductance that is affected when the instrument is coupled to the coil.
 3. The assembly of claim 1, further comprising a receiver containing the coil.
 4. The assembly of claim 1, further comprising a processor operably connected to the coil and configured to determine if the instrument is coupled to the coil.
 5. The assembly of claim 1, wherein the instrument is a first instrument, the prong is a first prong, and further comprising: a second instrument configured to be removably coupled to the coil, the second instrument having physical dimensions differing from the physical dimensions of the first instrument; and a second prong having a length corresponding to the physical dimensions of the second instrument.
 6. The assembly of claim 5, further comprising a processor configured to determine if the first instrument, the second instrument, or no instrument is coupled to the coil.
 7. The assembly of claim 6, wherein the processor is configured to identify the physical dimensions of the first instrument based on the length of the first prong and the physical dimensions of the second instrument based on the length of the second prong.
 8. The assembly of claim 1, wherein the instrument assembly is configured to be connected to the transmitter of a surgical navigation system.
 9. A surgical navigation system, comprising: a transmitter; and an instrument assembly communicating with the transmitter, comprising: a coil having an interior space; an instrument configured to be removably coupled to the coil; and a prong affixed to the instrument and configured to be at least partially disposed within the interior the coil when the instrument is coupled to the coil, wherein the prong has a length corresponding to the physical dimensions of the instrument.
 10. The system of claim 9, wherein the instrument is a medical instrument configured to be placed within the body of a patient.
 11. The system of claim 10, wherein the transmitter is connected to the body of the patient and the transmitter cooperatively operates with the coil to provide data relating to the location and orientation of the coil with respect to the transmitter and the body of the patient.
 12. The system of claim 11, further comprising: a processor operatively coupled to the transmitter and to the coil; and a display operatively coupled to the processor; wherein the processor is configured to generate an image of the location of the instrument with respect to the body of the patient using the data relating to the location and orientation of the coil.
 13. The system of claim 9, wherein the coil has an inductance that is affected when the instrument is coupled to the coil.
 14. The system of claim 9, further comprising a receiver containing the coil.
 15. The system of claim 9, further comprising a processor operably connected to the coil and configured to determine if the instrument is coupled to the coil.
 16. A method for identifying interchangable instruments, the method comprising: providing one or more instruments, each of the one or more instruments having a prong of a length corresponding to the physical dimensions of the one or more instruments; providing a receiver configured to be coupled to the one or more instruments, the receiver having a coil with a depth; and identifying if the one or more instruments is coupled to the receiver based on the length of the prong when the one or more instruments is coupled to the receiver.
 17. The method of claim 16, wherein the prong of the one or more instruments is configured to at least partially fill the depth of the coil when the one or more instruments is coupled to the receiver.
 18. The method of claim 17, further comprising identifying the coupling based on the inductance of the coil.
 19. The method of claim 18, further comprising: providing a transmitter operatively coupled to a processor; and providing a display device operatively coupled to the processor.
 20. The method of claim 19, further comprising displaying a representation of the physical dimensions of the one or more instruments coupled to the receiver as it is oriented with respect to the transmitter.
 21. The method of claim 16, wherein the one or more instruments is configured to be used inside of the body of a patient.
 22. The method of claim 16, further comprising: uncoupling the one or more instruments from the receiver; coupling another instrument to the receiver; and identifying the other instrument based on the length of the prong in that other instrument. 